1. Field of the Invention
The present invention relates to a color filter, a method of producing the same, and a liquid crystal display device provided with the color filter.
2. Related Background Art
Recently, research and development of liquid crystal display devices as flat display panels have extended steadily, and the market of the liquid crystal displays is has been significantly scaled up.
Component materials used for forming a liquid crystal display device are roughly divided into a polarizing plate, a glass substrate, an oriented film, a liquid crystal material, spacers, a color filter, etc.
Of these materials, the color filter is relatively high cost and thus said to be a key point for enabling supply of a liquid crystal display device at a reasonable cost.
The color filter of a liquid crystal display device comprises a plurality of colored members having different levels of light transmittance, generally red (R), green (G) and blue (B) colored members, which are provided on a transparent substrate, each of the colored members functioning as a pixel.
Shield members are provided between respective pixels in order to increase display contrast. The shield members are generally known as a xe2x80x9cblack matrixmxe2x80x9d because the members are black. The black matrix is also provided on the substrate side opposite to the color filter.
The black matrix is generally formed by etching a chromium metal deposited film or sputtered film. The methods of forming the colored members which respectively form pixels include the method of dyeing a dyeable medium which is formed by photolithography, the method using a pigment-dispersed photosensitive composition, the electrodeposition method using a electrode pattern, and the low-cost method using an ink-jet process.
The method of producing the color filter by using the ink-jet process comprises simple production steps and is economically advantageous, as compared with conventional methods of producing color filters.
When a color filter comprising a plurality of colored members having different degrees of light transmission is formed, for example, inks of three colors R, G and B having different compositions are discharged for coloring.
However, this method frequently has the problem of causing height differences between the colored members (so-called height differences between colors) which respectively form R, G and B colors and which comprise ink dots. This is due to the fact that when the spectral characteristics of each of the R, G and B color inks are optimized, particularly, when an ink absorbing layer is used as an undercoat layer (ground layer), the undercoat layer swells depending upon the types and amounts of the coloring agents of R, G and B colors contained in the inks.
When a liquid crystal display device is assembled by using a color filter having such height differences between colors, the problem of inevitably deteriorating image quality occurs unless special attention is given to a protective film or the like. In general, an active matrix liquid crystal panel is required to have evenness of not more than 0.3 xcexcm, and particularly a simple matrix liquid crystal panel is required to have evenness of not more than 0.1 xcexcm.
As a method of solving this problem, a method has been proposed in which height differences are decreased by coating an evening layer on color pixel portions. However, with large height differences between colors, it is necessary to increase the thickness of the evening layer or forming a multilayer. In this case, this method possibly brings about the problem of decreasing transmittance.
Accordingly, an object of the present invention is to solve the above problems and provide a color filter having small height differences between respective color pixels, a method of producing the color filter having small height differences between colors at low cost, and a liquid crystal display device exhibiting high image quality.
Another object of the present invention is to provide a color filter requiring no thick evening layer and exhibiting high transmittance.
In order to solve the problems and achieve the objects of the present invention, in accordance with an embodiment of the present invention, there is provided a color filter comprising a plurality of colored members as pixel portions which are formed by using dots of a plurality of color inks having different spectral characteristics, wherein light transmitting ink dots other than the color ink dots are respectively formed on the pixel portions.
The present invention includes a method of producing the color filter, and a liquid crystal display device provided with the color filter.
In accordance with another embodiment of the present invention, there is provided a method of producing the color filter comprising at least the steps of forming dots of a plurality of color inks having different spectral characteristics on a substrate by an ink jet method to form a plurality of pixel portions, and forming light transmitting ink dots other than the color ink dots on the pixel portions.
In accordance with a further embodiment of the present invention, there is provided a liquid crystal display device comprising a first substrate on which the color filter of the present invention is provided, a second substrate having electrodes opposite to the first substrate, and a liquid crystal material disposed between the first and second substrates.
The aforementioned technical problems can be solved and the above objects can be achieved by the color filter, the method of producing the color filter and the liquid crystal display device provided with the color filter of the present invention.
Namely, since the color filter of the present invention has the light transmitting ink dots other than the color ink dots, which are respectively formed on the pixel portions formed by using the color ink dots, it is possible to remove or significantly decrease the height differences between respective pixels having different colors. This can remove or significantly prevent deterioration in image quality which is caused by height differences between colors. The color filter of the present invention also enables achievement of high transmittance because of no need for an evening film.
The method of producing the color filter of the present invention is capable of providing an optimum color filter at a low cost.